There is a vast scope for this type of network; it extends from the medical field, which has a high number of interconnections, to the aerospace field where the need for reconfiguration is of paramount importance. These networks also have numerous applications in the field of computers where the network reconfiguration times are a limiting factor as well as in the distribution of data in the radar antennas. Other examples of applications will be described below.
The use of light to convey information has become more widespread since it can be used to carry a considerable amount of information. The need for reconfigurable networks makes the choice of switching element critical. In the known state of the art, reconfiguration is carried out by various means. For example, the optical switch, positioned on the optical fiber network and based on the switching of optical beams guided in the fibers either by liquid crystals or by mechanical movement of optical fibers. However, the high reconfiguration time (from several hundred microseconds to several milliseconds) makes this system unsuitable for datacom applications. In addition, one optical fiber is required for each transmitter. The use of an electrical switch upstream from the transmitters makes reconfiguration faster but one transmitter is required for each reconfiguration combination, and there again, the network is multifiber.
FIGS. 1A and 1B describe two networks of the prior art in which the light beams can be carried by a single optical fiber. The first example (FIG. 1A) describes an optical time division multiple access (OTDM) multiplexer. The network comprises a set of transmitters EMi and receivers REj. In the remainder of the description, the index “i” refers to transmission and the index “j” refers to reception. In this example, the indices i and j take values from 1 to 4. Each transmitter comprises electrical/optical conversion means EO and an optical switch OS. When the switch is closed, a brightness-modulated light signal is output from a digital data signal DATAi and transported by optical transport means, in this example an optical fiber FO, to receivers REj, themselves formed from an optical switch OS and optical/electrical conversion means OE. Each receiver is associated with a user USERj. Reconfiguration is carried out by time management of the switches. However, the disadvantage of this simple, low-cost system is that the users are allocated a reduced useful passband, because of the time division. Moreover, perfect synchronization is required between transmitters and receivers.
FIG. 1B illustrates a WDM (Wavelength Division Multiplexing) type network for which the reconfiguration is carried out in wavelengths. The wavelength multiplexing technology consists of injecting into the same optical is fiber FO several optical signals (or channels) with the same modulation frequency but with different wavelengths (λi). Reconfiguration is then carried out by choosing the color corresponding to the required path. This technology can therefore be used to carry a large number of signals at the same time. However, it requires the use of special transmitters and receivers, marked respectively EMi and REj on FIG. 1B, which have all colors, for example by using tunable laser sources for the transmitters and tunable filters for the receivers, as well as special components for the multiplexing. Consequently, the system is too expensive for datacom applications.